Hydrocracking process

ABSTRACT

CATALYST POISONS PRODUCED BY HYDROTREATING OF ORGANIC NITROGEN-CONTAINING HYDROCARBON OILS, ARE REMOVED BY CHEMICAL TREATMENT WITH ACIDS OR ACID COMPOUNDS RESULTING IN SUBSTANTIAL IMPROVEMENT IN SUBSEQUENT HYDROCRACKING.

United States Patent O US. Cl. 208-90 6 Claims ABSTRACT OF THE DISCLOSURE Catalyst poisons produced by hydrotreating of organic nitrogen-containing hydrocarbon oils, are removed by chemical treatment with acids or acid compounds resulting in substantial improvement in subsequent hydrocracking.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to catalytic hydrocracking. More particularly, the invention relates to an improved hydrocracking process in which catalyst life is increased by chemical removal of heavy-boiling catalyst deactivators from the hydrocracking feed.

Discussion of the prior art Hydrocracking is a well-known process for the conversions, in the presence of hydrogen, of petroleum stocks into lower boiling distillate fuels. The process has found wide application because of its inherent flexibility and is employed to produce light gases, gasoline, distillate fuel, such as jet fuels, as a selective method of producing lubricating oils having particular properties, etc. In the main, however, the greatest application is the production of distillate fuels. For these applications, high-boiling refractory feeds boiling above the range of the desired products are customarily used. For example, customary feeds include straight run gas-oils, residual oils and oils obtained from oil shale, tar sands, coal, etc.

Generally, those oils which are most suitable for upgrading by hydrocracking contain hetero-atom impurities such as organic sulfur, nitrogen, oxygen and metallic compounds. Since all hydrocracking catalyst must contain both hydrogenation and acidic (for cracking) activity, and these activities must be maintained in reasonable balance, the nature of the feed to the process is a major factor in catalyst stability and life, i.e., operability without regeneration. Nitrogen compounds have long been recognized as detrimental to catalyst life. In addition, very high-boiling condensed polycyclic compounds are detrimental be cause of their pronounced tendency to form coke deposits on the catalyst.

Customarily, hydrocracking processes use two reaction stages wherein the first stage functions primarily to convert heteroatomic compounds (e.g., organic nitrogen compounds to NH;,) prior to the principal cracking reactions in the second stage. Thus, first-stage catalysts and operating mode are generally chosen for resistance to sulfur and nitrogen poisoning, for high hydrogenation activity and relatively low cracking activity. In case of very high hetero-atom containing feeds, the feed may be hydrofined even prior to the first hydrocracking stage.

Some catalysts, however, have sufficient resistance to nitrogen and sulfur poisoning to allow their use in both the first and second stages. Even with these catalysts, different conditions are employed in each stage to compensate for organic nitrogen compounds.

In most hydrocracking processes hydrogen sulfide and ammonia, from the hydrogenation of organic sulfur and nitrogen compounds, are removed from the gas stream Patented Apr. 20, 1971 (principally hydrogen) after the first stage and prior to the second stage. In two-stage hydrocracking it is often advantageous to also remove some converted oil between stages.

Thus, up to a certain level (determined by the feed, catatyst, operating conditions and desired products) the feed may be cracked in the first stage. Peck et al., US. 3,360,457, issued December 1967, describes such a process. Using this technique the first-stage cracked product may be removed, as by fractionation, and the reactor size of the second stage accordingly reduced or conversely the overall capacity of a given size plant increased. As can be seen, definite advantages accure from partial conversion in the first-stage reaction zone.

It has now been discovered that when petroleum oils are first treated to convert organic nitrogen compounds to amomnia (i.e., denitrification), certain high-boiling components are formed in the oil which seriously reduce the effectiveness of the subsequent cracking catalyst. It has also been found that these catalyst poisons can be selectively removed by contacting the oil with an acid or acid compound, thereby producing an insoluble sludge which can be physically removed.

SUMMARY OF THE INVENTION In broad aspect, my invention is an improvement in a plural-stage hydrocracking process wherein an organic nitrogen-containing petroleum oil is first treated in the presence of hydrogen and a suitable catalyst for conversion of organic nitrogen compounds to ammonia and subsequentially hydrocracked in a cracking reaction zone, the improvement comprising acid treating at least a portion of first catalytic zone effluent to form a hydrocarbonaceous sludge and removing the sludge prior to further cracking of the efiluent.

Hydrocarbon oils suitable as feed to the process of the invention are, for example, middle distillates, gas oil fractions, cycle stocks, pyrolysis gas oils and the like. Suitable feeds can also be obtained from oil shale, hydrogenation of coal and the like. In general, the hydrocarbon oil feed will contain at least about 10 p.p.m. (by weight) nitrogen compounds and boil within the range from about 350 F. to about 1050 F. and preferably from about 550 F. to about 900 F.

According to the process of the invention the hydrocarbon oil is first treated for denitrification and if desired for initial cracking.

The effluent oil from the denitrification reaction zone is usually separated from the reaction gas. Ammonia and/or other contaminant gases are removed from the predominantly hydrogen gas stream. However, removal of gas is not an essential feature of the present invention.

The first stage effiuent may also be fractionated and a portion of the higher boiling fraction passed to the second catalytic stage. This is especially useful when the firststage is operated to accomplish both cracking and denitrification. It is, moreover, in this situation where the present invention achieves a most pronounced advantage. The amount of catalyst poisons increases substantially with in creased severity in the first reaction stage and in feeds which have been previously converted as by non-hydrogenative catalytic cracking, severe thermal cracking or pyrolysis. In general, for the process of the invention at least the portion of the first stage effluent boiling above about 500 F. is acid treated for removal of catalyst poisons and then passed to the cracking reaction stage.

For removal of the catalyst poisons, the first-stage efiluent or at least a portion thereof is contacted with an acid capable of complexing or polymerizing carbonaceous poisons into an insoluble sludge. Contacting may be carried out at any suitable conditions of temperature and pressure as will be obvious to those skilled in the art. However, it is preferred that the acid treatment be con ducted at as close to prevailing conditions of the effluent as possible. That is, it is advantageous to treat at the temperature and pressure of the effiuent material to minimize heating, cooling and depressuring and repressuring loss. The conditions will, however, be dependent upon the nature and amount of acid used.

The components present in first-stage effiuent which account, at least in part, for rapid catalyst deactivation are highly condensed, multi-ring aromatics, many of which are colored and usually cause a characteristic orange-red color of the effluent liquid. Compounds con taining seven or more condensed rings have been identified as the predominant poisons.

Acids which are suitable include strong mineral acids and Lewis acid compounds. Thus, strong acids such as H 50 H PO and the like may be used, but it is preferred, when using strong acids, that concentrated acids be avoided. For example, While concentrated H 80 is effective in complexing the undesirable polycondensed poisons, it reacts rapidly and results in difficulties in phase separation of the sludge and oil. Thus, for example, 60% of H 80 and 85% of H PO were found to be very effective and favorable in phase separation.

Lewis acid compounds are also effective agents. A Lewis acid, in conformity with conventional nomenclature, is a compound in which the normal electronic grouping about the central nucleus or atom is incomplete, and, thus, the central atom can accept an electron pair or pairs from a Lewis base, which is any compound capable of donating an electron pair or pairs.

Specific examples of suitable Lewis acid compounds are tin tetrachloride, aluminum tricloride, antimony tribromide and molybdenum acetylacetonate.

The amount of acid which is used depends, inter alia, upon the acid used. For example, when using aqueous solutions of mineral acids, such as sulfuric or phosphoric, sufiicient acid should be used to enable good contact between the aqueous acid phase and the oil phase. For aqueous acid solutions about 1% or more solution, basis hydrocarbon treated, is used. Good results have been obtained with, for example, 8% acid. In general, between about l% w. to 25% acid basis hydrocarbon is suitable.

When Lewis acids are used, smaller amounts sufiice. Thus, with Lewis acids, such as tin tetrachloride or aluminum trichloride, about 0.05 to 2% w. acid, basis hydrocarbon treated, is sufficient. While larger amounts are not thought to be chemically detrimental, the use of large quantities of these compounds unnecessarily complicates handling and separation.

The process of the invention is employed in the hydrocracking of organic nitrogen-containing hydrocarbon oils Where the nitrogen is at least partially converted to t ammonia in the presence of a catalyst having cracking activity. In general, the process is most appropriate in more or less conventional dual stage hydrocracking processes where the feed is converted in a first reaction zone to effect organic nitrogen and sulfur removal. The process, i.e., the chemical removal of hydrocarbonaceous poisons, becomes increasingly beneficial as the severity in the first reaction zone increases. Severity is determined by the temperature, pressure and space velocity used. Thus, for example, severity increases with increased temperature due to reduced pressure or increased space velocity. When refractory feeds are processed, e.g., those containing high boiling heteroatomic impurities, to low impurity levels, high temperatures and low space velocities are required; such operation is characterized as severe.

Denitrification conditions are preferably as follows: temperature between 250 C. and 475 C.; space velocity between 0.4 and volumes of oil per hour per volume of catalyst; pressure between 500 p.s.i.g. and 2000 p.s.i.g.;

4 ratio of hydrogen to oil between about 1500 and 30,000 standard cubic feet of hydrogen per barrel of oil (s.c.f./b.).

If a very active catalyst is used in the first reaction zone milder conditions are employed to obtain no more than the desired degree of conversion. On the other hand, if the catalyst in the first reaction zone is less active, more severe conditions must be selected.

The hydrocracking catalyst used in either zone comprises a hydrogenation component and an acid-acting cracking component. The hydrogenation component is preferably one or more metals of the Groups I-B, VIB or VIII of the Periodic Table of Elements and/ or their sulfides and/or their oxides. Preferably, the hydrogenation component is one or more of the metals cobalt, nickel, tungsten, molybdenum, platinum, palladium, cop per and/or silver and/ or the sulfides and/ or oxides thereof. The amount of hydrogenative metal is generally about 0.1 to 25% w.

The cracking component can comprise any one or more of the active, acidic cracking catalysts such as the siliceous refractory oxides, including synthetic components as well as acid treated clays and similar materials, or crystalline alumino-silicates known in the art as molecular sieves. In general, the synthetic siliceous cracking catalysts are preferred and include, for example, silicaalumina, silica-alumina-titania, silica-magnesia, silicaalumina-magnesia, silica-alumina cracking catalysts containing from about 90% silica and from about 30- 10% alumina are highly suitable. The preparation of synthetic siliceous cracking catalysts is well known in the art.

The hydrogenation component and the acidic cracking component can be composited in any suitable manner including, for example, impregnation of the cracking component with the hydrogenation component, cogellation of the hydrogenation component with the synthetic cracking component, or by ion-exchange of hydrogenation metal ions into the cracking component. For ion-exchange, the cracking component may be in the form of a hydrogel or a xerogel. The final composite is usually calcined, reduced in an atmosphere of hydrogen or snlfided to obtain the appropriate active form. In some cases the active form may be a complex of the hydrogenation component with the acidic cracking component. Promoters, such as fluorine, are often included.

The hydrocracking reaction is highly exothermic and therefore the usual practice is to provide multiple beds of catalyst in either one or more vessels. To avoid excessive temperatures in the reaction zone, means are usually provided in the catalytic Zone for cooling, such as by the injection of appropriate quantities of relatively cold feed, recycle oil, hydrogen, or the like. Hydrogen is generally used as this not only provides cooling but replaces hydrogen consumed in the reaction and thus maintains hydrogen partial pressure at desirable levels.

The following examples serve to further illustrate the practice and advantages of the present invention, but are not to be taken as a limitation thereof.

Example l.-A catalytically cracked heavy gas oil was hydrotreated under mild conditions to reduce the initial organic nitrogen content from 645 to about 3 ppm. The conditions were: 1500 p.s.i.g. pressure, 1.0 LHSV (volume liquid/hr./volume of catalyst), 9H /oil mole ratio and temperature of 370 C. The catalyst was an Ni/W on silica-alumina containing 11% w. Ni and 16% w. W. The silica-alumina contained 77% w. Si and 23% w. alumina.

This hydrotreated oil is representative of a first reaction zone product in which the first reaction stage is operated for denitrification with little or no cracking.

To a portion of the oil, a small amount of tin tetrachloride (about 0.1% W.) was added. An insoluble sludge immediately formed and was removed from the oil (by filtering) as a tarry residue.

This feed was then tested for hydrocracking (representative of severe second reaction stage hydrocracking) at 1800 p.s.i.g., 1.5 LHSV, H /oil ratio to achieve a 67% conversion of feed to lower boiling product, and using an aged Ni/W/F on silica-alumina hydrocracking catalyst (4.5% w. Ni, 3.0% W. W and 2.2% w. F).

After 80 hours the temperature required to malnta conversion at 67% was 338 C.

The same hydrotreated feed (not treated with tin tetrachloride) required a temperature, under the same COIldltions, of 345 C. Thus, the treatment resulted in a 7 C. temperature advantage indicative of substantially improved catalyst activity due to reduced poisonlng. It should be noted that at 7 C. higher temperature 1s P' proximately equivalent to a 50% reduction in required space velocity.

Example 2.Another catalytically cracked heavy gas oil was given a more severe dentrification treatment (higher conversion temperature) using an aged, fairly deact1- vated Ni/W/F on silica-alumina catalyst (16.6% w. W; 8.7% w. Ni and 2.1% w. F). The treated oil contained about 3 ppm. organic nitrogen and had a red/amber color which is sometimes associated with severe hydro treatment.

Hydrocracking this oil at 1500 p.s.i.g., 0.67 LHSV, 10/1 H oil to obtain a 67% conversion over an Ni/W/F on silica alumina catalyst (4.6% w. Ni; 3.2% w. W and 3.2% w. F) required a temperature of 287 C. after 80 hours of operation.

A portion of this oil was contacted with a small amount of tin tetrachloride at about 25 C. A sludge formed and was filtered, the total removed being about 0.2% w. basis oil. The treatment eliminated the red/amber color of the oil.

Hydrocracking this cleaned oil required a temperature of only 270 C.an advantage of 17 C. Contacting with tin tetrachloride at 200 C. was as effective in formation of sludge as at 25 C., thus ensuring that the oil cleaning in a two-stage hydrocracking process can be carried out without interstage cooling and reheating.

Example 3.Portions of the severely hydrotreated oil as described in Example 2 was separately contacted with aluminum trichloride, titanium tetrachloride, antimony tribromide and molybdenum acetylacetonate. All these Lewis acid compounds were elfective in forming a recoverable sludge and in removing the characteristic red/amber color.

Example 4.-A severely hydrotreated oil, as described in Example 2, having a red/ amber color, indicative of the presence of hydrocracking poisons, was contacted with various aqueous mineral acids.

A solution of 60% sulfuric acid removed the red/amber color and was efiiciently phase separated from the oil. A solution of concentrated sulfuric acid reacted extensively with the oil making phase separation difficult.

Phosphoric acid solution was also very successful. A solution of 85% phosphoric (140 gm. H PO as added to 1500 grams of oil. This treatment transferred 0.5 gm. of oil or about 0.03% of the initial oil into the acid phase. The red/ amber color was removed and the hydrocracking properties of the oil were greatly improved. Hydrocracking the oil treated with phosphoric acid was carried out under the conditions as described in Example 2. The temperature required to achieve 67% conversion was 276 C. compared to 287 C. for the untreated oil.

This result is obtained when only 0.03% of the oil is removeda result unattainable by physical separation (e.g., distillation) of the hydrotreated oil which necessarily involves greater removal of oil to achieve the desired results.

This experiment demonstrates the etficiency and selectivity of the method of the present invention.

It should be noted in all the above experiments, the improved hydrocracking results were obtained after only hours. Since the poisoning effect could expect to occur at the top of a hydrocracking catalyst bed and move through the bed, even greater long term benefits would be expected. Thus, not only does the method result in almost immediate benefit, but will also result in much improved catalyst life and operating cycle length (to a predetermined maximum temperature) in practical hydrocracking processes.

I claim as my invention:

1. In a hydrocracking process wherein an organic nitrogen-containing hydrocarbon oil having a boiling range above about 350 F. is subjected to hydrodenitrification in a first reaction zone followed by hydrocracking in a second reaction zone, the improvement which comprises: contacting at least the higher boiling portion of the first reaction zone effiuent with an acid compound to form a hydrocarbonaceous sludge with catalyst poisons created in the first reaction zone, and removing the resulting sludge prior to hydrocracking in the second reaction zone.

2. The improvement of claim 1 wherein the acid compound is selected from a group consisting of strong mineral acid solutions and Lewis acid compounds.

3. The improvement of claim 2 wherein the acid compound is an aqueous solution of H SO having a concentration below about 4. The improvement of claim 3 wherein the amount of acid solution used is between about 1 to 25% w. basis hydrocarbon oil treated.

5. The improvement of claim 2 wherein the acid compound is selected from a group consisting of the halides of Sn, Sb and Al.

6. The improvement of claim 5 wherein the amount of acid compound used is between about 0.05 to 2 w. basis hydrocarbon treated.

References Cited UNITED STATES PATENTS 2,970,105 1/ 1961 Condo et al. 208-295 2,973,317 2/1961 Watson 208-264 2,984,617 5/1961 De Chellis et al. 20888 3,095,368 6/1963 Bieber et al 208252 3,317,421 5/ 1967 Glcirn et al. 208264 DELBERT E. GANTZ, Primary Examiner R. M. BRUSKIN, Assistant Examiner US. Cl. X.R. 208-89 

